1306 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1956 



Helix-to-Waveguide Matching 



In the helix-to-waveguide transducer the hehx passes through the 

 center of the broad face of the waveguide and energy is coupled between 

 helix and waveguide by an antenna and matching taper. A capacitive 

 coupler on the helix and an rf choke on the waveguide place an effective 

 ground plane at the waveguide end of the antenna. The rf choke also 

 assists in minimizing leakage of rf power. Details of this transducer are 

 shown in Figs. 5 and 14. 



600 



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 Q 



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a. 



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 z 



o 



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UJ 

 HI 



o 



550 



500 



450 



400 



- 350 



LU 



300 



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LU 



cc 



D 



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Q- 



LLI 



1- 



250 



200 



150 



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10 15 20 25 



POWER INPUT TO HELIX IN WATTS 



Fig. 16 — Comparison of heat dissipation properties of different helix struc- 

 tures. In this experiment, the helices were heated by passing dc current through 

 them while they were mounted in a vacuum. The temperature was determined 

 from the change in helix wire resistance. 



Along with the results for glazed and non-glazed helices in a normal round 

 envelope, this figure shows results on a structure consisting of a glazed helix in an 

 envelope which has been shrunk around the helix support rods. This technique 

 produces a structure which, l)y virtue of the good thermal contact between the 

 support rods and the envelope, can dissipate more power than the conventional 

 structure. The additional complication of shrinking the envelope is not necessary 

 for the power levels used in the IM1789. However, this method could be used if it 

 were necessary to extend the tube's output range to higher power levels. 



